Amphibian epithelial and morphological adaptations to dry habitats: a preliminary survey of adaptive trait variation among Colombian dry forest anurans. Thesis dissertation presented by: Juan Salvador Mendoza Roldán Director: Dr. Andrew J. Crawford. Universidad de Los Andes, Bogotá, Colombia. 2014. Resumen: Los anuros poseen una organización dermal simple que ha evolucionado para solucionar los problemas atribuidos a la terrestrealizacion. La innovación estructural como la aparición de glándulas con un amplio espectro de secreciones y la presencia de regiones especializadas, altamente vascularizadas han permitido la supervivencia de los anuros adultos en ambientes secos, dominados por altas temperaturas y la presencia de sustratos y corrientes de aire desecantes. Estas especies muestran adaptaciones tegumentarias para la perdida de agua, que van desde la presencia de osteodermos y co-osificación craneal hasta el uso de secreciones de origen lipídico. Estas adaptaciones morfológicas se encuentran acopladas con rasgos etológicos y ecológicos que configuran la estrategia adaptativa de la especie. La presente contribución se enfoca en la caracterización básica de las estructuras del tegumento, por medio de microscopia de luz. Se comparó la variación de caracteres discretos entre poblaciones y en algunos casos especies hermanas presentes en hábitats húmedos y secos. Se probó el efecto de algunas variables climáticas sobre el tamaño corporal para establecer el valor adaptativo de las diferencias intra e inter especificas existentes entre proporciones de la tibia y el cráneo, medidas relacionadas con la relación superficie y volumen. Las comparaciones realizadas entre poblaciones hermanas de distintos orígenes geográficos y de hábitat se realizaron para describir la relación existente entre algunos aspectos de la morfología externa, histología características pluviométricas, haciendo énfasis en la biota anfibia de uno de los ecosistemas terrestres más amenazados de Colombia, el bosque seco tropical. Abstract: Anurans possess a very simplified dermal organization, which has evolved to solve the basic problems of terrestrialization. Structural innovation, presence of specialized highly vascularized regions and gland sets with a wide diversity of secretions, have allowed adult anurans to survive in desiccating environments that are dominated by dry substrates and air currents, in places with elevated day temperatures; geographically this places may be generalized by having extended periods with no rainfall thus dominating dry conditions. These species show interesting integumentary adaptations to avoid water loss that range from the presence of osteoderms and skin co ossification to the use of lipid based impermeable secretions, generally these morphological adaptations are coupled with behavioral traits that together configure the adaptive strategy of the species. The present contribution focuses on the examination of anatomical components configuring the dermal organization of some Caribbean dry forest species, and by means of light microscopy characterize the basic structure of species integument to compare variation of discrete traits among conspecific populations and in some cases pairs of dry and wet habitat sister species. Body size variation was tested to establish the adaptive value in water economy conferred by body proportions related to the total surface to volume ratio. Body proportions included the analysis of variation between sibling populations, where total lengths (SVL) were contrasted with Tibial length and Craneal width. Comparisons among conspecific populations from different geographical and habitat related origin were made in order to describe the basic relation between external morphology, histology and the habitat rainfall category (Dry or Wet), focusing on the frog biota from one of Colombia´s most threatened land ecosystem the Seasonally dry tropical forest. Introduction: The colonization of terrestrial habitats by amphibians begun in the end of the Devonian period 360 million years ago, when freshwater Rhipidista with lobed fins, migrated from pond to pond during the dry season, behavior that aided in the survival of water dependent animals, with physiological boundaries for free dwelling on terrestrial ecosystems (Toledo et al. 1993; Romer, 1959). Dehydration always will be the earliest of amphibian problems; many fossil species show the presence of scales and bony plates that favored water retention (Colbert, 1969 in Toledo et al. 1993). Present amphibians are poorly adapted to strict terrestrial life, their skin is a very simple dermal integument that does not generally serve as a barrier to the flow of water from and towards the amphibian body, creating two mayor selective pressures crucial in the evolution of modern amphibians; aquatic species tend to hydrate and loose inner solutes and terrestrial forms tend to dehydrate by means of evo transpiration (Porter 1972). The morpho-physiological interaction of amphibians with their abiotic environment is a complex and dynamic system of related process, arid habitats such as dry forests, deserts and open shrub lands and savannas, impose a rigorous environmental filter that has caused morphological, physiological and behavioral evolution of a wide diverse of adaptive traits that function in synergy to configure independent overall adaptive strategies for each member of the anuran community (Toledo et al. 1993; Duellman and Trueb, 1986). Amphibians don not drink the water required for metabolic function (Ex. Phyllomedusa), this water penetrates their bodies, principally by the way of the integument , special zones for rehydration are present in different zones of the amphibian body, reason why skin permeability to water differs from one part of the animal to the other (Toledo et al. 1993). This author also concludes that Inter and intra specific variation among skin traits may be related to adaptation for a particular environment, and this variation may confer structural differences in the integuments. Canziani and Cannata (1980) have shown that arid region Ceratophrys ornata, has a smooth ventral skin except in the pelvic region, where it is granular, on the other hand Individuals from moist temperate climates have uniformly granular ventral skin; while dehydrating arid area frogs may lose less water, but moist area frogs are better rehydrating by the presence of a granular skin. Skin thickness and the number of epidermal skin layers vary across amphibian species, in the process of keratinization a process related with the aquatic or terrestrial environment. Interspecific analyses have shown that species from the African genus Ptcychadena have an inverse relationship between body size and skin width, with the largest having the thinnest skin (Le Quang Trong, 1975). Other genus such as the African Phrynobatrachus, show variable skin thickness related to diversity of habitat, forest species have thinner skins than do savanna species of the same size, and ubiquitous species have a skin thickness intermediate to these two (Le Quang Trong, 1971). Skin gland density per square millimeter of skin is greater in the savanna-dwelling than in the forest dwelling species of frogs, in savanna species there is a predominance of mucous glands, these produce mucous secretions that help the animal in its adaptation to high temperatures and low relative humidity environments (Le Quang Trong, 1975). Mucous production depends directly on gland density and it has been shown that the mucous protects against desiccation. These Mucous glands are important in thermal and water economy relationship of the frog and its environment, mucous discharges aid in the control of body temperature and also maintain the amphibian skin moist for cutaneous respiration. The secretions produced by serous cutaneous glands in the order Anura exhibit highly variable ultrastructural features (Delfino et al. 1992). Serous storage bodies represent a hetorogenous class of structures ranging from vesicles containing translucent products to dense membrane bounded aggregates; their morphological variation also includes accumulations resembling multivesicular bodies. This heterogenity reflects specific biosynthetic pathways during the post golgian maturation phase which can be easily seen in the premetamorphic stages of development, mature serous products are consistent for each species in each genus investigated (Delfino 1991). Daly et al. (1987) comment that the wide variability in both composition and function of serous secretions of anuran skin reflects evolution of the survival strategies in the living families. Species from genus Phyllomedusa are known for exhibiting great polymorphism in their sereous gland morphology, studies performed by G. Delphino et al. (1998), show that variation of size and histochemical properties vary among species present in Argentina. Phyllomedusa species possess at least three serous gland types that have been classified on base of morphological and histochemical characterization. Skin permeability has been found to be greatly influenced by cutaneous lipids (Schim and Bardem, 1965). Blaylock et al. (1976) described peculiar glands in Phyllomedusa. These glands named as lipid secreting glands, were proved to be related with regulating evaporative water loss through the skin, frogs from this genus spreads lipids over the body surface using all limbs with a stereotyped whipping behavior (Blaylock et al.1976). Arboreal hylids are potentially more exposed to dehydrating conditions,